Why do we measure leaf chain?
When a forklift truck leaf chain is in mint condition, the rivet pins and articulating link apertures are almost perfectly cylindrical in shape and, especially in high quality leaf chain, have a very smooth surface finish.
This ideal state has excellent bearing properties which are necessary for smooth, quiet and efficient operation. It is inevitable, however, that a forklift truck chain will wear leading to the deterioration of these properties. When the rivet pins wear (a process known as Galling), they become castellated as seen in the picture below. Furthermore, the apertures in the link plates elongate, also seen in the photo below.
Most leaf chain rivet pins are produced with a case hardened outer surface. It is generally accepted that a 3% worn leaf chain will lose approximately 18% of its tensile strength.
Over time the castellations will become so deep that the case hardening of the leaf chain rivet pin will be completely destroyed. Once the surface has worn away it will become considerably weaker and potentially very dangerous. It is, therefore, necessary to limit the level of acceptable leaf chain wear.
The FB professional chain wear gauge (CWG) is a precision tool that has been purposely designed for the accurate measurement of chain wear in leaf chain/forklift chain. It states in the accompanying instructions that at a percentage elongation of 2% the chain will need to be carefully monitored if it is to be still used. At 3% elongation, the chain is considered a safety risk and should be replaced immediately.